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© 2010. Hobart Institute of Welding Technology EW512-6 Nondestructive Testing Methods

Nondestructive Testing Methods

Training Workbook EW-512-6

Written by

the Staff of Hobart Institute

of Welding Technology

Additional copies can be obtained from:

Hobart Institute of Welding Technology400 Trade Square East

Troy, Ohio 45373

www.welding.org

(937) 332-5433

© 2009. Hobart Institute of Welding Technology, 400 Trade Square East, Troy, Ohio, U.S.A.

All rights reserved.

Printed in the United States of America.

ISBN: 978-1-936058-23-5

iii



iv

TABLE OF CONTENTS

TOPIC PAGE

Glossary of Welding Terms v

Introduction to Nondestructive Testing Methods 1

Principles of Visual Testing 7

Principles of Penetrant Testing 13

Principles of Magnetic Particle Testing 19

Principles of Ultrasonic Testing 25

Principles of Radiographic Testing 30

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TOPIC 1

INTRODUCTION TO NONDESTRUCTIVE TESTING

OBJECTIVE

To be able to dene and identify the purpose for nondestructive testing and the symbols used to indicate

INTRODUCTION

This section includes an overview of nondestruc-

tive testing, its purpose, the basic principles in-

volved with the most common types, giving a de-

scription of the symbols used to indicate methods

of inspection.

Nondestructive testing is an evaluation process in

which no damage occurs to completed welds or

to the surrounding structure provided the proper

procedures are followed. It is used to qualify pro-

cedures, welders, and to monitor the quality of

production welding.

Nondestructive testing, whether in the shop or

eld, can be used for detecting small discontinui-

ties and defects quickly and effectively. The most

common methods for nondestructive testing are:

Visual

Penetrant

Magnetic particle

Ultrasonic

Radiographic

ene ran es ng

Visual Testing

Magnetic Particle Testing

1




When choosing an inspection method, take into

consideration the advantages and limitations of the

method.

The sensitivity of each method reects its ability to

respond to a discontinuity’s size, shape and loca-

tion. Visual inspection is limited to discontinuities

exposed to the surface. Radiographic inspection

could be used to detect discontinuities on or below

the surface. The method to employ is based largely

on the degree of quality required for the weldment.

For example, to verify quality, visual or magneticparticle inspection may be all that is required for low

pressure piping, whereas high pressure piping may

require radiographic testing.

Cooperation between design, welding, and quality

engineers is required to determine which testingmethods to use in order to meet the testing require-

ments of the weldment.

Once the decision is made, it becomes the quality

assurance engineer’s responsibility to provide the

qualied inspector with the details of the inspection

requirements, so the weld can be inspected cor-

rectly.

Radiographic Testing

Ultrasonic Testing

Magnetic Particle Testing

2




Methods of indicating inspection type will be nec-

essary when nondestructive testing is required.This is generally done on engineering drawings by

the use of nondestructive testing symbols and writ-

ten procedures.

II. NONDESTRUCTIVE TEST

SYMBOLS

Nondestructive testing symbols are standardized

much like the symbols used for welding. A refer-

ence line is used in the same manner as welding

symbols, and is as long as necessary for adding

information.

An arrow is used to direct the information to the de-

sired location. It can be placed at either end of the

reference line, pointing up or down, on either sidewhere welds are to be placed.

The side of the joint the arrow points to is referred

to as the “arrow side”. The opposite side is called

the “other side”. It is important because it species

which side of the welded joint is to be inspected.

3

Other side Arrow side

Other side

Arrow side

MT 6

RT 25%

1

411

1

411

PT

PTPN-17

GTAW

45

45

1

4

1

4




4

The symbols use initials to indicate the test

method to be used. They are:

VT = visual testing

PT = penetrant testing

MT = magnetic particle testing

UT = ultrasonic testing

RT = radiographic testing

When the test symbol is located below the

reference line, it signies that inspection is to be

performed on the arrow side of the joint. When

placed above the line, it indicates the inspection

is to be performed on the other side.

The test symbol can be placed on both sides of

the reference line to indicate that each side of the

weld is to be inspected.

The symbol is centered between a break in the

reference line when it doesn’t matter on which

side the inspection is to be performed. In all

cases, the inspection is for 100% of the weld

unless otherwise noted.

Details, such as testing procedures, specication,

processes, or other pertinent information are

sometimes placed at the end of the reference line

inside a “tail bracket”.

When less that 100% of the length is to be

inspected, it can be specied by a section length

or percentage located to the right of the symbol.

The required sections or areas are usually

specied in the written procedures. When no

percentages are noted, 100% of the weld is to

be checked.

VT

PT

Other side Arrow side

Other si

Arrow si

Other side

side

Other side

Arrow side

Arrow

Other side

Arrow side

Arrow side

Other side

RT + PT

RT

UT

RT

A-12

MT 6

RT 25%




5

The all around test symbol is used when the in-

spection is to be performed completely around a

welded joint.

The number of tests to be performed is indicted

in parenthesis. The symbol shown here species

four applications of magnetic particle inspection.

Multiple reference lines are nondestructive test

symbols combined with other nondestructive or

welding symbols. The order in which operations

and tests are performed is indicted by the order of

the lines. The rst operation is the closest to the

arrow.

This multiple reference line shows a single

Vgroove weld with melt through to be inspected

on the arrow side with a combination of visual and

radiographic testing methods. Visual inspection is

performed on the other side. Inspection details are

located in procedure T-28.

The engineering staff can provide information for

welding and inspection using symbols and notes

on the engineering drawings.

Knowledge of the testing methods, procedures,

and the symbol elements, can enable you to bet-

ter understand this common language and help to

maintain higher quality at lower cost.

MT

(4)

RT + PT

RT

1

2

3

VT + RT

VTT28

T

( (

( (

O t h e r

A r r o w

O t h e r

s i d e s

B o

t h

s i d e

Basic testing symbol Arrow

Test-all-aroundsymbol

Test in field

Length of sectionto be tested

(N)

Number of tests

Reference line

Tail

Specificationor other reference

L




6

TOPIC 1

REVIEW QUESTIONS

1. Dene the purpose of nondestructive testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. Where are nondestructive symbols placed?

_______________________________________________________________________________________

_______________________________________________________________________________________

3. List the common methods of nondestructive testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

4. How long should the reference line of a nondestructive test symbol be?

_______________________________________________________________________________________

_______________________________________________________________________________________

5. An arrow is used to direct the information to:

_______________________________________________________________________________________

_______________________________________________________________________________________

6. The side of the joint the arrow points to is called the:

_______________________________________________________________________________________

_______________________________________________________________________________________




TOPIC 2

PRINCIPLES OF VISUAL TESTING

OBJECTIVE

To be able to identify the basic principles and applications of visual testing.

INTRODUCTION

Visual testing is the most popular and widely

used nondestructive testing method. It consists

of examining weld and overall weldments and

comparing the evaluation to a set of standards.

When correctly applied, it is an effective method of

quality control insuring conformance to a procedure

and allowing errors to be corrected. This leads to

production of a higher quality weldment at reduced

costs.

Visual inspection practice requires the inspector to

be familiar with all duties which apply to inspection,

such as:

• Learning to read blueprints

• Having a knowledge of welding

• Processes specication

• Procedures and workmanship standards

The inspector must be capable of making:

• Responsible judgments

• Accurately recording data

• Writing concise reports

Even though visual testing is the simplest method

of performing inspections, detailed written procedures

are needed to ensure proper application of the

inspection.

7




PREWELD INSPECTION

To perform preweld inspection, an inspector be-

comes familiar with all aspects of the job, such as:

• Material specication

• Bill of materials

• Welding procedures

When completely familiar with all the written de-

tails, the inspector compares the dimensions of

all the parts, checking dimensions to engineering

drawings, and verifying tolerances of parts to en-

sure proper nal t-up of the weldment.

The inspector examines the joint preparation and

surface conditions of the materials for proper

cleaning and lack of aws. Poor t-up, contaminat-

ed base metal surfaces, improper equipment, and

incorrect settings can lead to weld discontinuitiesor defects.

If backing is specified, it should be in accordancewith the job specifications and be correctly and

securely fastened. The tack welds become part

of the finished weld and should meet the same

soundness requirements.

Preweld inspection should include examining

the equipment to insure it is in proper operating

condition.

8




9

IN-PROCESS VISUAL INSPECTION

In-process welding begins with:

• Verifying specied procedure

• Observing welds during production

• Deleting problems before completion of

welds • Observing welder skill

• Verifying proper interpass temperatures

• Assuring interpass cleaning requirements

are met

• Comparing each pass or layer to a sample

workmanship standard

VISUAL TESTING OF FINISHED

WELDS

The inspector should compare the nished welds

or weldments to the engineering drawings or

specications. This assures:

• Proper part dimensions

• Weld size

• Weld location

• The correct amount of welds on the

weldment

Accuracy of the measurement is more important

than the method of measuring. A good-looking

weld could be rejected if it is not the correct size.

Tools, such as high-low gage, let weld gage, or a

scale can be used to measure correct dimensions.

Another part of post-weld inspection is the exami-

nation of the weld surface. Common discontinui-

ties visible to the surface area are:

• Cracks

• Porosity

• Overlap

• Arc strikes

• Undercut

• Spatter




Each of these problems has allowable limits

described in the applicable code or inspection

procedure.

After welding, the weldment may also reveal base

metal defects such as delamination, cracking,

or excessive distortion, which should be clearly

marked for repair.

Documentation of visual testing begins once

all aspects of before, during, and after welding

inspection has taken place. This consists of the

inspector evaluating the results to decide whether

the welds or weldments meet the prescribed

specication.

The inspector must make reports of every detail

and keep complete records. Generally, any items

which do not meet the requirements are noted and

described. Any repairs made during production

should be reported.

Good record keeping is essential. Whenever such

detailed records are required, they are normally

signed or certied by the fabricator, and copies are

sent to all persons entitled to receive them.

10




11

Visual inspection is an invaluable quality controltechnique. Caution must be taken before drawing

conclusions.

Welds with good surfaces are often good quality,

but surface appearances will not prove careful

workmanship took place.

To be reasonably sure of weld quality, all phases of

visual inspection must be accomplished.




12

TOPIC 2

REVIEW QUESTIONS

1. The visual inspector must be capable of: (list three)

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. To perform “preweld inspection” the inspector must be familiar with: (list three)

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. List four things an inspector must check for when performing “in-process” visual inspection.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. List four things the inspector should check on the nished welds or weldments.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

5. Any items not meeting the test requirements are:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________




13

TOPIC 3

PRINCIPLES OF PENETRANT TESTING

OBJECTIVE

To identify the basic principles and applications of penetrant testing.

INTRODUCTION

Penetrant testing is a highly sensitive method used

for detecting discontinuities which are less likely to

be detected by visual inspection. A aw such as a

ne crack open to the surface could go undetected

during visual examination, but would be exposed

with the proper application of the penetrant test.

A unique characteristic of penetrant testing is

its capillary action. It is the ability of a liquid to

redistribute itself into or between closely tted

surfaces. This allows a aw or discontinuity to be

detected.

Liquid penetrant has certain limitations. Generally,

it cannot be used on materials with very porous or

highly absorbent surfaces. These materials couldlikely give false indications.

The two basic types of liquid penetrant testing are:

• Fluorescent

• Visible dye

Both types have several variations, but share the

same basic procedures. They are the application

of a liquid penetrant, the removal of the excessive

penetrant, and the application of a developer to

draw penetrant from any openings in the surface.




14

The main concept of both types of penetrant is to

read the contrasting colors. For example, when

uorescent penetrant is applied to a surfacecontaining a defect or discontinuity, the solid

surface will appear as a deep violet. The aw will

show up as a yellow-green glow under an ultraviolet

light. This is the most sensitive method.

Visible dye penetrant appears as a bright indication

on a white background. It is easy to apply and is

performed under normal lighting conditions.

The surface should be cleaned before applicationof the penetrant. There are several methods of

cleaning. Precaution should be practiced when

performing these cleaning operations because

they involve chemicals. They may be highly

ammable or toxic if inhaled.

Some cleaning methods such as grinding, chipping,

machining, or shot blasting can prevent parts from

being accurately inspected because discontinuities

can be hidden by these procedures.




15

The penetrant is applied after the proper

cleaning procedures have been completed. It

can be applied by dipping, brushing, or spraying

the area to be tested. The most portable method

is by pressurized spray cans.

WATER WASHABLE PENETRANT is a dye

placed in a water-based solution. For nonporous

materials, it provides the lowest sensitivity

because of the ease of penetrant washout of

shallow openings.

POST EMULSIFIABLE PENETRANT is a

dye placed in an oil-based solution. The post

emulsifiable variation needs an application of

an emulsifier to chemically break down the oil

base of the excessive penetrant to render it

water washable. For shallow surface openings,

it allows for greater sensitivity because the

penetrant remains in the openings as the

emulsifier is washed away.

SOLVENT REMOVABLE PENETRANT remains

the most popular. It is usually applied by a

spray can to the inspection surface. Then, after

a specified time, known as the dwell time, it is

removed from the surface with a solvent on a

cleaning cloth, leaving the penetrant trapped

below the surface intact. When performed

correctly, it can reveal ultra-fine openings only a

few micro-inches in size.




16

APPLY VISIBLE DYE PENETRANT

Step 1

Penetrant is applied to a properly cleaned surfaceby brushing, dipping, or spraying. The method ofapplication is based on the amount and size of thepart being inspected

Step 2

Allow sufcient dwell time so the penetrant canenter any openings. Dwell time is based on the typeof material and the degree of accuracy required.

Longer time allows penetrant into smaller openings.Refer to the testing procedure or manufacturer’srecommendation for dwell time (usually 5 minutesto several hours).

Step 3

Remove the excess penetrant by the appropriatemeans. When using water washable penetrant,rinse excess with a spray of water. Watertemperature and angle of spray should be speciedin a written test procedure. This avoids washing outof penetrant.

When using the post emulsiable penetrant,emulsier dwell time should be monitored so onlyexcess penetrant is removed.

Step 4

After the surface is properly cleaned and dried,

the developer is applied. The blotter action ofthe developer draws out the penetrant left in anyopenings in the test area.

Wet developers are powders suspended in liquid.They can be applied by dipping, brushing orspraying.

Dry developer is in powder form and is dusted onthe test surface.

The pressurized spray can is the most portablemethod of applying penetrant, cleaner, anddeveloper.




17

It is important to apply a smooth and even coating

over the surface. Avoid heavy layers of developer.

Thick coverings might obscure small indications.

Allow for correct dwell time. The developer generally

takes about one-half the penetrant dwell time or

whatever is recommended by the procedure.

Step 5

Examine and record test data drawn from the

results of the penetrant test.

FLUORESCENT DYE PENETRANT

INSPECTIONThis type of penetrant testing is done in the same

way as visible dye penetrant, except a uorescent

light source is needed to read the results after the

dwell time on the developer has elapsed.

GENERAL INFORMATION ON

PENETRANT INSPECTION

When penetrant inspection is performed on

multipass welds, the penetrant must be thoroughly

cleaned between every pass. Welding over test

solutions could create discontinuities.

Penetrant testing is an invaluable quality control

technique. Like visual testing, care must be taken

in drawing conclusions. The depth of a aw cannot

reasonably be measured. The inspector can only

see penetrant indications that appear on thesurface.

The larger the aw and the longer the time allowed

for penetrant bleed out, the larger the indication will

appear.

In conclusion, remember that the proper application

of this test is based on the steps discussed and by

following the details of the written test procedures.




18

TOPIC 3

REVIEW QUESTIONS

1. List two surfaces liquid penetrant cannot be used on:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. Dye placed in a water-based solution is called:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. List three methods of cleaning to avoid when using penetrant testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. What precautions must be followed when performing penetrant testing on multi-pass welds?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________




19

INTRODUCTION

Magnetic particle testing is a highly sensitive

method used for locating:

• Cracks

• Porosity

• Slag inclusions

• Other discontinuities in materials and

welds which can be magnetized

A simple bar magnet can simulate this testing

method. When a small amount of magnetic

particles are placed on a bar magnet, the particles

are attracted only to the ends, which are referred to

as the north and south poles.

If the magnet is notched, the magnetic lines of force

pass through the air, creating new north and south

poles on each side of the notch. Magnetic particles

will be attracted to the new poles.

When a part being tested is magnetized, the part

will act like a magnet. The magnetizing is done

either by passing a current through it or by placing

it in a strong magnetic eld.

TOPIC 4

PRINCIPLES OF MAGNETIC PARTICLE TESTING

OBJECTIVE

To identify the basic principles and applications of magnetic particle testing.




20

A surface aw or one slightly under the surface will

attract and hold the magnetic particles in a pattern

similar to the outline of the aw. Magnetic particles

can be applied by a dusting bag, atomizer, spray

gun, or brush depending on whether a wet solution

or dry powder is used. The particles in dry powder

form must be applied evenly and excessive particles

should be removed.

The wet solution provides a greater sensitivity for

ne surface cracks because it consists of a much

smaller particle size.

The dry powder remains more sensitive for aws

located below the surface.

This testing method is highly sensitive todiscontinuities open to the surface and becomes

less sensitive as the aw depth increases. This

method is sensitive to discontinuities down to one

quarter inch below the surface.

WET SOLUTION FOR

SURFACE DISCONTINUITIES

DRY POWDER FOR

SUBSURFACE DISCONTINUITIES




21

The two types of magnetic elds used are circular

magnetization and longitudinal magnetization.

The size and shape of the weldment to be tested

determines the type to be used.

Circular magnetization either passes a currentthrough the piece to create a eld, or creates a

eld in which a cylindrical part may be placed.

Longitudinal magnetization passes a current

around the piece to create a eld through the

piece.

Circular magnetization is provided by using a set ofprods. Walking the prods along the weld provides

full coverage. Extreme caution should be practiced

to insure that no arcing takes place between the

test surface and the prods.

Longitudinal magnetization can be applied by a

coil, a wrapped coil, or a yoke.

The yoke method is the most practical and widely

used method. It is also the safest because no

current comes in contact with the test surface

eliminating arcing on the surface.




22

Magnetic particle testing uses the different

characteristics of alternating current (AC) and

direct current (DC). Equipment availability and

degree of sensitivity required determine the type of

current to be selected.

Alternating current provides the least sensitivity

and magnetizes only the surface of the specimen,

instead of the entire thickness of the part.

Therefore, it should be limited to locating surface

discontinuities.

Direct current penetrates throughout the thickness

of the test specimen. It is the more sensitive of

the two currents, and is recommended for use on

welds when looking for subsurface discontinuities.

Visual evaluation is performed on all indications

represented by accumulated particles on the

surface.

The inspector evaluates the shape, sharpness,

width and height of the particle pattern to determine

the type of discontinuity or defect.




23

EVALUATION OF TEST RESULTS

Many factors should be taken into consideration in

order to make precise judgments. Careful evaluation

by a trained inspector is important. Decisions

should be based on requirements specied through

applicable specications, procedures, or codes.

Further nondestructive testing, such as ultrasonic

or radiographic may be required on a questionable

indication.

REPORTS AND RECORDS

A concise record of the test results should be

developed once all inspection has been completed.The clear transparent tape method uses clear tape

placed over the indication. This allows the particle

indication to be transferred to a test report form.

The tape with the particles stuck to the back is

placed over a simple sketch of the weldment.

A photograph of the tested surface may also be

taken and attached to the nal report.

CLEAN-UP OF TEST SURFACE

Demagnetizing a part may be necessary after all

reports are nished and visual inspection has been

performed. Some components may retain enough

magnetization to attract metal shavings, causing

excessive wear during service operations. It may

also make it difcult to have quality welds.

CONCLUSION

Remember that proper application of this test is

based on having qualied personnel to perform the

testing procedures and carefully following the steps

previously discussed.




24

TOPIC 4

REVIEW QUESTIONS

1. Name three discontinuities located by magnetic particle testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. The ends of a bar magnet are called:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. Which of the two types of electrical current (AC and DC) is the most sensitive?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. Once the inspection has been completed, what should be done?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________




25

TOPIC 5

PRINCIPLES OF ULTRASONIC TESTING

OBJECTIVE

To identify the basic principles and applications of ultrasonic testing.

INTRODUCTION

Ultrasonic testing is a highly sensitive method

used for critical applications where quality is very

important. This method is used for detecting:

• Cracks

• Inclusions

• Laminations

• Other discontinuities in welds and various

other materials.

The inspection method is similar in principle to the

sonar that military ships use to detect submarines.

The ship’s sonar device transmits inaudible sound

waves which reect off the submarine and are

received as signals on a screen.

Ultrasonic testing is performed in a similar manner.

A device called a transducer is coupled with the

part. It provides mechanical sound waves that are

transmitted into the weld or base metal to detect

aws.

Transducers are made in a limitless variety of sizes

and shapes. There are two common wave types,

the straight beam and the angle beam. The test

surface determines which transducer to use. The

angle beam is used where the reinforcement would

interfere. The angle beam can be placed to one

side of the weld. It produces no back reection. It

is important in detecting discontinuities and aws inpipe and tubing welds.




26

Couplants eliminate the air gap between the

transducer and the specimen. A variety of liquidsor pastes are used to insure proper transmission of

the sound waves.

Sound waves travel into the specimen and, if

interrupted or reected, the transducer will receive

an echo. The signal is sent to the ultrasonic unit

where it is amplied and displayed on a screen.

While the display screens of early ultrasonic units

used a cathode ray tube or CRT, more moderndisplay screens are liquid crystal display or LCD.

The display consists of a straight base line. When

sound waves are interrupted, a break will appear

on this base line. These breaks are referred to as

vertical pips. An inspector interprets these pips to

determine aw depth and location.

The large pip appearing on the left is called the

initial pulse. It represents the top surface of the

specimen. Sound waves travel through and are

reected back to the transducer. The pip to the

right is called the back reection. It represents thebottom surface of the specimen.




27

The aw depth and location can be displayed by

any pip signals that appear between the initial

pulse and back reection. When a transducer is

moved across a block with a pre-drilled hole at

three inches in depth, all pips will appear at the

three-inch mark on the scale.

The amplitude or height of the pip will give some

indication of the size of the aw. The higher the pip,

the larger the reected area of the aw.

ADVANTAGES AND LIMITATIONS OF

ULTRASONIC TESTING

When compared with other nondestructive testing

methods, some of its most outstanding features are

accurately determining aws, depths and location;

it can be used on practically all nonporous metals

or materials; and battery operated equipment

makes it ideal for eld applications.

The ultrasonic method of inspection requires a

highly trained and skilled operator and it is difcult

to contact test complex congurations and rough

surfaces.




28

Equipment must be carefully calibrated prior to use.

Calibration is normally done by using a standard

reference block.

VARIATIONS

Immersion testing is another variation similar to

the contact method. It is used quite often in testingof larger components. This test is conducted with

both the transducer and component submerged in

water. The water acts as a couplant allowing the

signals to be transmitted into the part.

The aircraft industry uses this method for testing

irregular or complex-shaped components.

CONCLUSION

Ultrasonic testing can be a very valuable tool for

inspection of weldments provided the proper

equipment is used, personnel are well-trained, and

properly written tests are used.




29

1. List three discontinuities that can be detected by ultrasonic testing:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. What are the two types of transducers?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. When compared to other nondestructive testing methods, ultrasonic testing’s most outstanding feature is:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. What are two disadvantages of ultrasonic testing?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________




30

INTRODUCTION

Radiography is a sensitive method used for

detecting aws found in castings, welds, and

various metal structures.

It is the most reliable form of nondestructive

inspection, used extensively in the welding

industry for critical situations, such as pipewelding and pressure vessels. This inspection

method is similar to s-rays used by hospitals to

detect a broken bone.

The x-ray machine sends invisible radiation

through the body to a sheet of photographic lm

similar to photographic lm used in cameras.

Since bones absorb more x-rays than the

surrounding esh, they appear lighter on the

developed lm. Breaks show up darker because

x-rays pass through them more easily.

TOPIC 6

PRINCIPLES OF RADIOGRAPHIC TESTING

OBJECTIVE

To identify the basic principles and applications of radiographic testing.




31

RADIOGRAPHIC TESTING

Radiographic inspection of welds is done with

a similar x-ray generating machine or with a

radioactive material called isotopes. These

generate higher energy gamma rays.

It provides data for a more exacting evaluation anda permanent record in the form of a photographic

image called a radiograph.

When radiation is passed through the item being

tested, aws appear lighter or darker than the

surrounding metal.

A radiograph of a piece of metal with varying

thicknesses will show up on the processed lm

as different shades of darkness. The thinner

materials show up darker because it allows more

energy to reach the lm.

The amount of radiographic energy absorbed is

based upon the material’s mass or density. For

example, when steel and aluminum blocks of the

same size are exposed to the same intensity of

radiographic radiation, the aluminum will cause

a darker image because it isn’t as dense as the

steel and absorbs less energy.




32

An internal aw, such as scale, trapped slag, or

porosity will show up as a darker area on the lm.

When evaluating these indications, care must be

exercised. False images can be caused by dirt,

static electricity, or poor lm processing, leading

to the wrong conclusion.

Because of many variables such as exposure,

intensity of radiation and lm-processingtechniques, a device called an image quality

indicator (IQI), or penetrameter, is often used. It is

placed on the object being radiographed, usually

off to one side of the desired weld section.

There are two basic types if IQIs: hole type and

wire type. Hole type penetrameters are usually

rectangular pieces of material with the same

radiograpic absorption as the material being

tested. They vary in thickness and have a series

of holes with different diameters. Wire type

penetrameters use wires of varying diameters.

With both types of IQIs, the sensitivity of a

radiographic image is determined by which of the

holes or wire diameters is visible.

A densitometer measures the lm density. This

indicates if the correct lightness or darkness of the

lm has been achieved in order to better detect

aws during interpretation.




33

The success of radiographic inspection depends

greatly upon the training and experience of the

operator.

SAFETY

Radiographic inspection must be performed by a

qualied operator because of the potential dangersfrom radiation which can cause death or serious

injury if safe practices are not followed.

Do not enter areas where x-ray or gamma raysources are used without permission or supervision

of an experienced radiographer.

For gamma ray methods, the radioactive isotopes

are always on or emitting radiation. The must

be stored and transported in special containers

referred to as pigs. Isotopes should be used only

by a qualied radiographer. Radiation detecting

devices must be worn in order to detect radiation.

Examples of such devices are survey meters and

special lm badges.

CONCLUSION

All aspects of radiography must be handled

only by an experienced operator who knows the

importance of safety and has the skill to interpret

results and maintain proper records.




34

TOPIC 6

REVIEW QUESTIONS

1. Name two critical situations where radiographic testing is used:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

2. The amount of radiographic energy absorbed is based on:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

3. Name three things that can cause “false” images on a radiograph:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

4. The device used to obtain the proper exposure on a radiograph is called a:

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________



GLOSSARY OF WELDING TERMS

Acceptable weld - A weld that meets the

applicable requirements.

Arc strike - A discontinuity resulting froman arc, consisting of any localized remelted

metal, heat affected metal, or change in the

surface prole of any metal object.

Backing - A material or device placed

against the back side of the joint adjacent

to the joint root, or at both sides of a joint

in electroslag and electrogas welding, to

support and shield molten weld metal. The

material may be partially fused or remain

unfused during welding and may be either

metal or nonmetal.

Backing strip - Backing in the form of a

strip.

Codes - A system of principles or rules.

Complete fusion - Fusion over the entirefusion faces and between all adjoining weld

beads.99

Contaminants - Implies intrusion of or con-

tact with dirt or foulness from an outside

source, making the piece unt or unclean.

Crack - A fracture type discontinuity char-

acterized by a sharp tip and high ratio oflength and width to opening displacement.

Crater - A depression in the weld face at

the termination of a weld bead.

Defect - A discontinuity or discontinuities

that, by nature or accumulated effect, ren-

der a part or product unable to meet mini-

Discontinuity - An interruption of the typical

structure of a material, such as a lack of ho-

mogeneity in its mechanical, metallurgical,

or physical characteristics. A discontinuity isnot necessarily a defect.

Fillet weld - A weld of approximately trian-

gular cross section joining two surfaces ap-

proximately at right angles to each other in a

lap joint, T-joint, or corner joint.

Interpass temperature - In a multipass

weld, the temperature of the weld area be-

tween weld passes.

Joint design - The shape, dimensions, and

conguration of the joint.

Overlap - The protrusion of weld metal be-

yond the weld toe or weld root.

Porosity - Cavity-type discontinuities formed

by gas entrapment during solidication.

Procedure - The detailed elements of a pro-

cess or method used to produce a specic

result.

Slag inclusion - A discontinuity consisting

of slag entrapped in weld metal or at the

weld interface.

Welding procedure qualication record

- A record of welding variables used to pro-

duce an acceptable test weldment and the

results of tests conducted on the weldment

to qualify a welding procedure specication.

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